1. Field of the Invention
This invention relates to charged particle beam columns, and more specifically to a system for generating charged particle beams from a light image.
2. Description of The Related Art
In the field of electron beam (or charged particle beam) lithography, a beam of, e.g., electrons from an electron source is directed onto a substrate. The electrons expose a resist layer (in this case an electron sensitive resist) on the substrate surface. Typically electron beam lithography is used for making masks; however it can also be used for direct exposure of semiconductor wafers.
One technique to generate an electron beam image is to expose a photocathode with a light image, whereby the photocathode converts the light image into a demagnified electron beam image. One problem with the use of a photocathode is variations in the photon-to-electron conversion ratio of the photocathode, which in turn cause dose errors in a charged particle image written on the mask or wafer. Hereafter xe2x80x9celectron conversion factorxe2x80x9d means photon-to-electron conversion ratio of the photocathode. Such variations are due, for example, to particulate contamination, chemical contamination, and overexposure of a local area of the photocathode.
Thus what is needed is a method and apparatus to generate charged particle beam images using a photocathode with reduced variations in the electron conversion factor.
One embodiment of the present invention provides a beam conversion system that includes: a photoconverter on which is incident a light image, that converts the light image into a charged particle beam; and a displacement device coupled to move the photoconverter, where the light image illuminates a moving surface of the photoconverter.
Thereby an embodiment of the present invention provides a method of generating a light image, the method including the acts of: generating a light image; directing the image onto a moving photoconverter, whereby the image is incident on a moving surface of the photoconverter device; and converting, at the photoconverter device, the image into an electron emission pattern which is imaged on the surface of a mask or wafer.
Various embodiments of the present invention will be more fully understood in light of the following detailed description taken together with the accompanying drawings.